Metal dust and process of making the same



MayZZ, 1923. 1,456,035

M H. NEWELL METAL DUST AND PROCESS OF MAKING THE SAME Filed Sent. 25 1918 WITNESS INVENTOR N. /7. NE WELL,

' H/5 ATTORNEYS w generallv Patented May 22, 1923.

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MINTON NEWELL, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR TO THE ALLOYS COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALIFORNIA.

METAL DUST AND PROCESS OF MAKING THE SAME.

Application filed September 23, 1918. Serial No. 255,314.,

To all whom it may concern:

Be it known that I, MINTON H. Nnwnnn, a citizen of the United States, and a resident of the city and count of San Francisco and and a better product. The invention is of articular value in the manufacture of zinc Zinc dust is largely used in a number of arts, but the characteristics measuring its efiiclency have not been fully understood. An object of this invention is to produce a zinc dust in vela fine particles generall uniform in size an spherical in shape. eretofore zinc dust has been comparatively in-- eflicient' because known processes of manufacture have resulted in products which comprised particles too large in size or particles vary in size and shape to a large extent. I have discovered that by vaporizing the metal and condensing the vapor in the man ner hereinafter recited, it is practicable to' obtain a roduct composed of particles of extreme neness and uniformity and oxidized to only such an extent as not to interfere with the increased efficiency. The zinc dust of my invention is particularly eflicient when a used as a precipitant in the cyanide process of recovering precious metals.

The manufacture of zinc dust comprises,

va orizin zinc and condensing 'the vapor f vfiiileit' as been usual to vapor- 1ze the zinc in zinc ore, I prefer to use in this process zinc metal, slag, drowes, skimmings, residues or by-products of zinc metalcaLprocesses or" any suitable z nc-bearmg material. If the vapor -therefrom iscorh densed in the air, the result is zinc oxide. If

the vapor is condensed without air, the result.

is particles too large for efiicient use. And

60 either of theseresults may be observed in some of the particles obtained byl followin' suggestions heretofore made. I ave foun that by giving proper attention to the supply a of air in relation to the volume and tempera ture of the vapor, the difliculties are avoided and a superior product more expeditiously obtained.

To accomplish the result satisfactorily, it 3 is desirable to suppl to the vapor a carefully regulatedsupp of air, avoidin on the one hand, comp ete exclusion 0 air from the condensing chamber which would result in too large particles) and, on the other hand, an excessive amount of air in the condensing space or any part thereof (which would result in too much oxidation of the particles or some'of them). This regulation of the supply of air maybe accomplished by any means of'admission which prevent any sudden inrush to any part of the condensing chamber. I have found that the apparatus hereinafter described aflords one way of accogplishing it successfully and automatica y.

It is preferable also to give attention to the 76 v heat of the vapor in connection with the regulated supply of air for limited oxidation. Because oxidation takes placemore readily at high temperature, the supply of .air should reach the vapor first at that point where it has parted with much of its latent heat. It is, accordingly, desirable to make use of a condensing chamber large enough to afford a cooling space and to admit the air at a point of comparatively low temperature therein. I

In the accompanying drawing the apparatus described in my said application Serial N o. 117 ,430, filed August 29, 1916, is shown as illustrating one convenient instrumen- P0 tality which'may be availed of for practisin the process. The zinc-bearing material, preferably in the metallic form and with or with out a quantity of carbon or other reducing agent, 1s placed in a 'retort'2, which is arran ed in a furnace 3 so that it can be heated to e required temperaturetand in the apparatus which I have constructed, I emplo oil as fuel. The neck of the retort exten s throug'lh'the furnace wall and makes a tight j oint -erewith and projects into a large neck 4 on the cohdeisrfigshttmber 5 and the joint large in diameter so that the vapors passing from the retort will not be directed into con-. tact therewith, since such contact has a tendency to form metallic zinc instead of zinc dust. The chamber is preferably formed of metal andis in thermal contact with the air so that the heat therein may be dissipated. The chamber is preferably conical at its lower end and is provided with a gate-controlled outlet 7, for the discharge of the dust. The chamber is provided with an aperture 8, preferably arranged on the side opposite the retort, which is covered with a bag 9 of suit- 10 able fabric, as for instance,.woolen flannel.

When vapor is discharged through the aperture, the bag the pressure 1s relieved the bag collapses. As the process is being carried on the bag pulsates continuousl The position of the aperture isfpreferabl y such that when thebag is removed, a stirring rod may be passed therethrough and into the retort.

When the process is practised by the use of such apparatus a limited amount of air is presented to the vapor and contact of too much air with any part of the vapor (as might occur, for example, by permitting a sudden inrush of air to any part ofthe condensing chamber on condensation) is avoided. This limited quantity of air is moreover presented to the vapor first at a point where the vapor has parted with some of its latent heat. The result is a dust, the particles of which are extremely fine and uniform and oxidized to a limited extent, the oxidation being insufficient to interfere with the successful use of the product in the arts. By regulating the supplyof air, the

I percentage of oxidation may be accurately controlled to obtain a product best suited 'for the particular purpose in view.

The provision made for elasticity in the condensation chamber enables the vapor to 40 be properly separated from contact with too much oxygen during the period of condensation without creating such-conditions of pressure or otherwise as result in condensation into comparatively large particles. The maintaining of a proper equilibrium between the vapor, air and temperature at the time of condensation results in great uniformity of product and rapidity of production, as well as a more efiicient article. 4 The standard method of determining the efficiency of zinc dust as aprecipitant for old or silver from cyanide'solutions is the harwood method, set forth in the'Journal of the Chemical, Metallurgical and Mining Society of South Africa, vol. 12, No. 8 of page 332, February 1912, and reprinted in becomes distended and when.

250 cc. of the above solution with constant stirring. Continue stirring for ten minutes, and then stir violently every ten minutes for two hours. Filter rapidly and wash thoroughly, keeping precipitate in the beaker. Dissolve in '10 cc. nitric acid (C. P.) and wash all precipitate off of filter with as little water as possible. Boil ofl fumes, cool, dilute to 250 cc., add ferric indicator, and titrate with standard solution of a sulpho cyanide salt. Milligrams of silver found in this precipitate multiplied by the factor .0606 equals the precipitating efficiency when .5 grams of the zinc dust was used.

' The zinc dust'of my invention has an efficiency between 65% and and the greater portion of the zinc dust made by my process has an approximate efliciency of about 7 8% by the Sharwood method,- where- 35 as the maximum efficiency of other zinc dusts formed by the condensation of zinc vapor is below 65% and averages about 55%;

" I claim:

1. A. process for manufacturing metal dust, comprising vaporizing the metal and condensing the vapor in the presence of a limited regulated supply of oxygen.

2. A process for manufacturing metal dust, comprising vaporizing the metal, supplying to the vapor a limited amount of air, first contacting with a comparatively cool portion of the vapor, and condensing the .vapor in the presence of said supply of air.

3. A process for manufacturing metal dust, comprising vaporizing the metal, surrounding the vapor during the period of condensation with an elastic envelope adapted to expand and contract-according to the volume of vapor and prevent unrestricted access of air to any portion of the vapor, and condensing the vapor within such envelope.

4. A process for manufacturing metal dust, comprising vaporizing the metal, maintaining said vapor out of contact with an unrestricted supply of air to any portion thereof, admitting to the vapor a restricted supply of air varyingly in proportion to the varying volume of the vapor, and condensing the vapor" 5. A process for manufacturing zinc dust, comprising vaporizing the zinc, condensing the vapor and'oxidizing a portion thereof and cont plhngmthe oxidation V (SKA Zinc dust composed of exceedingly the Engineering and Mining Journal vok'fine particles substantially uniform in size 93, No. 19, page 943, May 11, 1912'. The Sharwood method as fo1lows:

In testing for zinc efiiciency a solution is prepared containing 8 grams of silver as potassium silver cyanide, 1.2 to 1.5 grams potassium cyanide, and .2 to .22 grams calcium oxide per liter. Emulsify .5 grams of the zinc dust with very little water, and add and substantially uniformly oxidized, such as results from condensing zinc vapor in the presence of a limited supply of air without unrestricted access of air to any portion of the vapor during condensation.

7. A zinc dust resulting from the conden-. sation of zinc vapor composed of substantially uniformly oxidized exceedingly fine 13o Sharwood method.

' 8. A zinc dust resulting from the condensation of zinc vapor composed of extremely fine particles of uniform structure, and having a precipitating efliciency above 70% as measured by the Sharwood method.

9. The process of manufacturing .zinc dust, which consists in vaporizing the zinc, surrounding the vapor durin the period of condensation with an enve op, supplying to the envelop a limited amount of air-first contacting with a comparatively cool portion of the vapor and condensing the vapor in the presence of the supply of air, whereby zinc oxide and very-fine zinc dust is formed.

In testimony whereof, I have hereunto set my hand at San Francisco, California, this 20 17th day of September, 1918.

MINTQN H. NEWELL. In presence of- 

